Why grow indoors
Growing indoors does three useful jobs on a homestead:
- Fresh greens in winter, when the garden is frozen or bare.
- Seed starting, so the outdoor garden gets a head start in spring.
- Food in a small space, such as a tiny house with little land.
What it does not do well is grow lots of calories. Potatoes, grains and squash need far more light and space than a home can easily give. Lesson 34 explains why that matters.
Light is the limit
Plants run on light. A sunny window in summer may be plenty. In winter, the days are short and the sun is low. Even a south window often gives too little light for strong growth, especially in northern climates.
A grow light is a lamp made to give plants the light they need. Most home grow lights now use LEDs, which use much less power than older types for the same light.
Lights need a schedule. Many seedlings and greens are grown with about 12 to 16 hours of light a day. Extension guides list the needs of each crop.
Text description
A side view of a two-level shelf for seed starting and greens. On each level an LED grow light hangs close above a tray of seedlings, shining straight down. The lights plug into a timer set for about 12 to 16 hours of light a day, which draws electricity mostly in winter, when solar output is lowest, so the lights belong on the load list. A small fan beside the shelf keeps air moving. Moisture rises from the plants into the room, so watch humidity and condensation on windows to avoid mold.
What a grow light costs in energy
Try a 100 W grow light for 14 hours a day. How much energy is that each day and each year?
300 Wh per day, which is 0.3 kWh.
Over a year: about 110 kWh, or 13 to 33 dollars at typical US grid prices.
Assumptions: Grid price range of $0.12 to $0.30 per kWh covers most US residential rates (EIA).
Off the grid, this matters. Grow lights run most in winter, when your solar output is lowest. That is the same squeeze as the heat pump in lesson 31. Add any lights to your load list from lesson 22.
What grows well inside?
Microgreens are vegetable and herb seedlings cut when they are just a few inches tall, often 1 to 3 weeks after sowing. They grow fast in a small tray.
Is each crop a good fit for indoor growing, or better left outside?
- Microgreens
- Basil, parsley and chives
- Lettuce and salad greens
- Potatoes for winter storage
- Winter squash
- Tomato and pepper seedlings for spring
- Corn
Seed starting
For many homesteads, the most valuable indoor growing is seed starting. You sow seeds in trays weeks before the last frost, then move strong young plants, called transplants, outside.
- Start seeds by working back from your last frost date. Seed packets and extension guides give the weeks for each crop.
- Give seedlings strong light close above them. Too little light makes tall, thin, floppy seedlings.
- Before planting out, harden off the seedlings. That means setting them outside for longer each day over about a week, so they adjust to sun, wind and cooler nights.
Hydroponics and aquaponics
Hydroponics means growing plants without soil. Roots sit in water with dissolved nutrients, or in an inert material like gravel or coconut fiber.
Aquaponics links fish and plants. Fish waste feeds the plants, and the plants help clean the water for the fish.
Both can grow a lot of greens in a small space. Both also need pumps, steady power, water testing and daily attention. A pump failure can harm plants or fish within hours.
Text description
Two simplified loop diagrams side by side. Left, hydroponics: a pump lifts water with dissolved nutrients from a reservoir up to a grow tray, where plant roots sit in the water or in an inert material such as gravel or coconut fiber, and the water drains back to the reservoir. Right, aquaponics: a pump lifts water from a fish tank up to a grow bed. The fish waste in the water feeds the plants, and the plants help clean the water, which flows back to the fish. In both, the pump needs steady electricity, the water needs testing, and a pump failure can harm plants or fish within hours. A note says full tracks on both are in Sprout and Fin, the sibling course.
This course does not teach these systems in depth. Sprout & Fin, our sibling course, has full hydroponics and aquaponics tracks. You can find it from our About page.
Moisture, power and trade-offs
Plants release water into the air. Many trays in a small, tight home can raise indoor humidity and lead to mold, as in lesson 11 (EPA). Keep air moving, and watch for condensation on windows.
Check
Your tomato seedlings on a windowsill are tall, pale and falling over. What is the most likely cause?
Summary
- Indoors is best for greens, herbs, microgreens and seed starting, not staple calories.
- Light is the limit. Grow lights use energy, mostly in winter, when solar is lowest.
- Harden off transplants before planting them out.
- For hydroponics and aquaponics, see Sprout & Fin, our sibling course.
Next, you will look at storing the harvest so it lasts through winter.
Go deeper: light intensity and duration
Plants respond to both how bright light is and how long it lasts. Growers sometimes describe the total as the daily light received, which combines intensity and hours. A brighter light for fewer hours can give a plant about the same daily light as a dimmer light for more hours, up to a point. Leafy greens need much less daily light than fruiting crops like tomatoes, which is one reason greens are the easy win indoors.